The proposed research will investigate the auditory detection, discrimination, and information processing mechanisms of fishes using a combination of psychophysical and single-unit neurophysiologcal methods. Recent behavioral and neurophysiological data show that much of the auditory processing among fishes is accomplished by central neural systems operating on the temporally codes representations of the acoustic waveform. The aim of this research is to define the characteristics of the central systems behaviorally, and to identify the patterns of neural activity which are correlated with, and perhaps determine, the behavioral capacities. Psychophysical experiments will focus on the variables affecting the detection and discrimination of stimulus envelope and temporal fine structure. Most recent studies have revealed that the goldfish auditory system does not temporally summate acoustic input in the way that mammalian and avian systems do, and that as a result, the ability to process the acoustic waveform in time. The fish's ability to detect amplitude modulation and to discriminate small phase changes in the waveform's fine structure appears to surpass that of the mammals. Neurophysiological experiments will focus on the response of single neurons of the 8th nerve and brain. Neural responses are analyzed in response to the same stimulus set used in the psychophysical studies in order to identify the information-bearing elements or the putative neural codes used in auditory processing. Most recent studies have suggested that inter-spike-intervals within single neurons carry much of the useable information to the brain of the goldfish.